Recursion method applied to a finite GaP cluster

The recursion method was used to study the local electronic structure of a ‘‘large’’ but finite system. The system is large in the sense that it is not practical to diagonalize the Hamiltonian numerically, but it is small enough that the local spectrum is strongly influenced by the size and shape of the system. The recursion method reduces the Hamiltonian into a ($a_n$,$b_n$) chain. We shall study those cases where the $a_n$,$b_n$ fluctuate indefinitely. Some important points on the implementation of the method are discussed. The method was applied to a cluster of Ga and P atoms. Special features in the electronic structure can be easily associated with specific local configurations of atoms. The results are typical of clusters of group III-V compounds.